1. Field of the Invention
The present invention relates to an angular velocity sensor used to detect an angular velocity acting on, for example, a moving object, such as a rotor, etc.
2. Description of the Related Art
In general, an angular velocity sensor of conventional technology as described in Japanese Unexamined Patent Publication No. 5-312576 and other publications is known.
The angular velocity sensor described in this Japanese Unexamined Patent Publication No. 5-312576 is in substance composed of a board, first and second vibrators, vibration generating means, and displacement detecting means.
The first vibrator is supported on the board through first supporting beams and arranged so as to be vibrated in the direction of a first axis horizontal to the board. Further, the second vibrator is supported on the first vibrator through second supporting beams and arranged so as to be vibrated in the direction of a second axis at a right angle to the direction of the first axis and horizontal to the board. Because of this, the second vibrator is able to be vibrated in the direction of the first and second axes in the state that the second vibrator is kept horizontal to the board.
Further, the vibration generating means provides vibration in the direction of the first axis to the first vibrator. In this state, when an angular velocity is applied around a third axis at right angles to the first and second axes, that is, a rotational axis vertical to the board, the second vibrator is displaced in the direction of the second axis by a Coriolis force in proportion to the angular velocity. Because of this, the displacement detecting means detects a displacement of the second vibrator in the direction of the second axis to detect the angular velocity.
In the above angular velocity sensor of conventional technology, when acceleration is applied in the direction of the second axis, the second vibrator is displaced in the direction of the second axis by the acceleration. At this time, the displacement detecting means also detects the displacement of the second vibrator by such acceleration as the displacement caused by an angular velocity. That is, even if the whole sensor is not rotated around the third axis vertical to the board, the angular velocity detecting means detects the displacement of the second vibrator when acceleration is applied in the direction of the second axis.
In this way, when acceleration is applied in the direction of the second axis, because the displacement of the second vibrator produced by the acceleration is added as noise, there is a problem that the detection accuracy of angular velocity is degraded.
The present invention can solve the problem associated with the above-mentioned conventional technology, and provides an angular velocity sensor which is able to detect an angular velocity applied around the third axis even if acceleration has been applied in the direction of the second axis.
The angular velocity sensor comprises: a board in the form of a flat plate; a rotational vibrator extended to the right and left from the central axis vertical to the board as the center of rotational vibration over the board and supported at the location of the central axis by rotational supporting beams so as to be rotationally vibrated; a first vibrator located on a right side of the rotational vibrator and supported by first supporting beams, a second vibrator located on the left side of the rotational vibrator and supported by second supporting beams; rotational vibration generating means for vibrating the second vibrator backward and forward when the first vibrator is vibrated forward and backward by giving rotational vibration to the rotational vibrator; a first displacement detector for detecting a displacement of the first vibrator vibrated to the right and left when an angular velocity is applied around the central axis of the rotational vibrator in the state that rotational vibration is given to the rotational vibrator by the rotational vibration generating means, and a second displacement detector for detecting displacement of the second vibrator vibrated to the right and left when an angular velocity is applied around the central axis of the rotational vibrator in the state that rotational vibration is given to the rotational vibrator by the rotational vibration generating means.
As thus constructed, when the rotational vibration generating means gives rotational vibration to the rotational vibrator over the board and makes the first vibrator vibrate backward and forward, the second vibrator is vibrated forward and backward. And an angular velocity is applied to the whole sensor around the rotational axis of the rotational vibrator in the state that rotational vibration is given to the rotational vibrator, a Coriolis force in proportion to the angular velocity acts on the first and second vibrators. At this time, as the first vibrator is vibrated backward and forward and the second vibrator is vibrated forward and backward, the Coriolis force acting on the first and second vibrators is in reverse, and the first and second vibrators are vibrated symmetrical to the right and left with respect to the central axis of the rotational vibrator. That is, when the first vibrator is displaced toward one side to the right and left, the second vibrator is displaced toward the other side to the right and left.
And when a displacement of the first vibrator is detected by the first displacement detector, a displacement of the second vibrator toward the other side is detected by the second displacement detector. Because of this, by using signals from the first and second displacement detector, the angular velocity applied to the whole sensor is able to be detected.
More, when acceleration toward one side to the right and left is applied to the whole sensor, the first and second vibrators are made to be displaced toward the other side to the right and left by this acceleration because of the inertia of the first and second vibrators. In this state, if an angular velocity around the central axis of the rotational vibrator is applied to the whole sensor, for example, the displacement to the right and left of the first vibrator is increased, and the displacement of the first vibrator is made equal to the addition of the displacement due to angular velocity and the displacement due to acceleration. On the other hand, the displacement to the right and left of the second vibrator is reduced, the displacement of the second vibrator is made equal to the subtraction of the displacement due to angular velocity from the displacement due to acceleration. Because of this, by adding detection signals from the first and second displacement detectors, the detection signals due to acceleration offset each other and only the detection signals due to angular velocity is able to take out.
The rotational supporting beams may be arranged in a spiral form between a supporting portion given at the central axis on the board and the rotational vibrator. In this case, the rotational supporting beams are able to support the rotational vibrator so as to give rotational vibration around the central axis by the whole rotational supporting beams being bent and deformed.
The first vibrator and the second vibrator may be arranged so as to be symmetrical to the right and left with respect to the central axis. In the case, when rotational vibration is given to the rotational vibrator, the first and second vibrators are able to be symmetrically vibrated to the right and left at the same speed. Accordingly, when the first and second vibrators are displaced by an angular velocity, the measure of the displacement is made nearly equal. Therefore, the amplitude of signals by angular velocity is able to be made nearly equal in the signals from the first displacement detecting portion and second displacement detecting portion.
More, the spring constants of the first and second supporting beams may be set to be nearly equal and at the same time the mass of the first and second vibrators is set to be nearly equal. In the case when acceleration is applied in the direction of a tangential line of the rotational vibrator, the first and second vibrators are displaced by a nearly equal measure. Therefore, without carrying out various operations, the displacement capacitance by acceleration is easily offset by using displacement signals from the first and second displacement detectors.
The rotational vibrator may have frame portions in the form of a rectangular frame on both of the end sides to the right and left. More specifically, the first vibrator may be composed of a first vibrating portion in the form of the letter xe2x80x9cHxe2x80x9d given inside a first of the frame portions, and the second vibrator may be composed of a second vibrating portion in the form of the letter xe2x80x9cHxe2x80x9d given inside a second of the frame portions. The first displacement detector may be composed of a first vibrating side electrode given in the first vibrating portion and a first fixed side electrode arranged inside the first frame portion. The second displacement detector may be composed of a second vibrating side electrode given in the second vibrating portion and a second fixed side electrode arranged inside the second frame portion. In this case, when rotational vibration is given to the rotational vibrator, the first frame portion is vibrated backward and forward, and the second frame portion is vibrated forward and backward. Therefore, the first and second vibrating portions are vibrated backward and forward in the reverse direction from each other.
And the first vibrating side electrode and first fixed side electrode detect capacitance between these first vibrating side electrode and fixed side electrode, and detect the displacement measure to the right and left of the first vibrating portion. Further, the second vibrating side electrode and second fixed side electrode detect capacitance between these first vibrating side electrode and first fixed side electrode, and detect the displacement measure to the right and left of the second vibrating portion.
The rotational vibration generating means may comprises first and second vibration generators located on the side of one end to the right and left of the rotational vibrator, separated in the backward and forward direction of the rotational vibrator, and giving backward and forward vibration to a first vibrator, and of third and fourth vibration generators located on the side of the other end to the right and left of the rotational vibrator, separated in the backward and forward direction of the rotational vibrator, and giving backward and forward vibration to a second vibrator. When the first vibrator is displaced forward by input of driving signals of the same phase to the first and fourth vibration generators given at the locations symmetrical with respect to the central axis, the second vibrator is displaced backward, and when the first vibrator is displaced backward by input of driving signals of the same phase to the second and third vibration generators given at the locations symmetrical with respect to the central axis, the second vibrator is displaced forward.
Because thus constructed, the first through fourth vibration generators are able to give rotational vibration around the central axis to the rotational vibrator. And the first and fourth vibration generators are arranged so as to be symmetrical with respect to the central axis and are driven at the same time by driving signals of the same phase. Therefore, when the first vibrator is displaced forward by the first and fourth vibration generators, the second vibrator is able to be displaced backward.
Further, the second and third vibration generators are arranged so as to be symmetrical with respect to the central axis, and are driven at the same time by driving signals of the same phase. Therefore, when the first vibrator is displaced backward by the second and third vibration generators, the second vibrator is able to be displaced forward.
Other features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiment (s) of the invention which refers to the accompanying drawings.